Jeffrey J. Kosowsky wrote:
What size conduit is needed to support 200A Mains supply?
(interested in the answer both for copper and aluminum)

Thanks

If this will be done in compliance with the US NEC then you would need
1&1/2" for copper or 2" for aluminum single phase dwelling service if
the conduit in question is schedule forty or eighty PVC. Many utilities
require schedule eighty PVC for service entry conductors but schedule
forty is allowed for the feeder between the service disconnecting means
and the main distribution panel.
--
Tom H